Evaluation of sampling methods for harvesting non-treated and hydrogen cyanamide treated kiwifruit vines

Abstract

From 1986 through to 1992 kiwifruit ( Actinidia deliciosa cultivar ‘Hayward’) from vines in the Bay of Plenty district of New Zealand, trained on a T-bar trellis with an upper wire to support renewal shoots, were harvested from various sections of vines and graded separately. For any variable, the effectiveness of grading only part of a vine was measured by R 2, the proportion of the variation in the true whole vine value that was accounted for by the estimate from the part vine. Grading fruit from ten long canes on the western side or all of the fruit on quarter vines gave R 2 values of approximately 0.6. R 2 values varied from 0.7 to 0.85 for half vines. Grading diagonal quarters was slightly better than using the east or west sides which were in turn marginally better than grading the north or south sides. In all of these cases the estimate was improved greatly when the part harvested was adjusted upwards by a scaling factor of the fruit weight on the whole vine divided by the fruit weight on the part graded. On hydrogen cyanamide treated vines, the west side of vines performed significantly better than the east side. This meant that a grading procedure based on one of these sides alone would be biased and could result in up to 22% error for vines growing on T-bars. Grading either the north or south side alone and adjusting by the fruit weight ratio was more satisfactory as the differences in fruit size at harvest were smaller between the north and south sides than between the east and west sides. In trials involving consecutive hydrogen cyanamide treatment of vines over five seasons, significant differences between the north and south sides of vines were observed in only one season but scaling by fruit weight overcame the problem.